The present invention relates to a cross-linkable composition and use thereof to thermally insulate pipe, preferably subsea metal pipe. The cross-linkable mixture comprises (i) an ethylene polymer, (ii) a silane, (iii) a polyfunctional organopolysiloxane with a functional end group, (iv) a cross-linking catalyst, and (v) optionally a filler and/or additive.

1. A process for insulating a metallic pipe or metallic equipment comprising the step of injection molding a coating on the pipe or equipment wherein the coating comprises a cross-linkable mixture comprising:

(i) one or more ethylene polymer,

(ii) one or more silane,

(iii) one or more polyfunctional organopolysiloxane with a functional end group,

4. The process of Claim 3 wherein the silane (ii) is copolymerized with ethylene in a reactor or grafted to an ethylene polymer by the use of a organic peroxide to provide a silane-grafted ethylene polymer.

5. The process of Claim 1 wherein the silane (ii) is a vinyl trimethoxy silane, an acryloxypropyltrimethoxysilane, a sorboloxypropyltriethoxysilane, a vinyl triethoxy silane, a vinyl triacetoxy silane, a gamma-(meth)acryloxy propyl trimethoxy silane, or mixtures thereof.

6. The process of Claim 1 wherein the polyfunctional organopolysiloxane (iii) is a polydimethylsiloxane of the formula:

wherein Me is methyl and n is from 10 to 400.

7. The process of Claim 1 wherein the polyfunctional organopolysiloxane (iii) is a hydroxyl-terminated polydimethylsiloxane containing at least two hydroxyl end groups, a polydimethylsiloxane having at least two amine end groups, or a moisture-crosslinkable polysiloxane.

8. The process of Claim 1 wherein the cross-linking catalyst is a Lewis or Bronsted acid or base.

9. A process for re-insulating the connected portion of two plastic-insulated metallic pipes comprising the steps:

(1) removing some plastic insulation from the end of each pipe,

(2) connecting the ends of the pipes together to form a circular connected region having an external diameter,

(3) fitting a split injection mold onto the connected region of the pipes, said injection mold having an internal diameter which is spaced from the external diameter of the of said connected region,

(4) injecting a cross-linkable polyolefin mixture into the cavity formed between said external diameter of the connected region and said internal diameter of the mold to obtain an injection- molded coating onto the connected region of the pipes, and

(ii) one or more silane, (iii) one or more polyfunctional organopolysiloxane with a functional end group,

(iv) one or more cross-linking catalyst,

and

(v) optionally one or more filler and/or additive.

Description:

METHOD FOR THERMALLY INSULATING SUB SEA STRUCTURES

FIELD OF THE INVENTION

This invention relates to the field of insulated pipelines and structures, and in particular to the field of subsea pipelines and structures and pipelines for use in deep water.

BACKGROUND OF THE INVENTION

For the construction of pipelines subjected to particularly aggressive environmental conditions, both for underwater and in the soil applications, plastic-insulated metallic pipes are widely used. To ensure that the plastic coating is not damaged by the welding operations to connect pipes, the plastic coating is removed in the region of the end sides of said pipes prior to welding and therefore, after two pipes have been connected, the uncoated connected parts have to be re-insulated in order to prevent external aggression (corrosion). In recent years, new methods for the re-insulation of the connected portion of plastic- insulated metallic pipes have been developed. Known processes for re-insulation of plastic- coated metallic pipes include several steps: pipe steel surface preparation, pipe steel heating, spraying of a primer, application of an adhesive polymer, application of a polymeric top layer. USP 6,843,950 describes a method for the application of a polymeric top layer onto the circular weld seams of pipelines formed by metallic pipes which are provided with a plastic insulating coating. Said method comprises fitting a split injection mold onto the connected pipes partially overlapping the plastic insulating layer of the pipes and injecting melted plastic material into the cavity formed between the mold and the outer surface of the pipes, whereby the melted plastic cools and solidifies thereby forming a sheath which is sealed to the existing plastic insulation coating of the pipes. Typically the melted plastic is injected into the mold with a pressure of less than 25 MPa and a temperature not exceeding 230°C. The injection-molded re-insulating sheath is normally more than 10 mm thick in the region not overlapping the existing insulating layer. In order to easily and quickly fill the molds, plastic materials, in particular thermoplastic propylene polymers, known in the art to be suitable for the use in injection-molding processes, should have relatively high melt flow rates. Polyolefin compositions for injection molding are disclosed for example, in

WO2004/003072, said polyolefin compositions comprising a crystalline propylene homo- or copolymer and a copolymer of ethylene with an alpha-olefin having 4 to 10 carbon atoms and having melt flow rate higher than 20 g/10 min. EP1456294 discloses polyolefin compositions having relatively high melt flow rates and a good balance of properties, such as flexural modulus and impact resistance, said compositions comprising a crystalline propylene homo- or copolymer and a blend of a propylene/ethylene copolymer and an ethylene/C4-Cio copolymer.

However, existing insulated pipelines comprising one of the above mentioned insulating materials, while demonstrating a number of significant advantages, can still have certain limitations, for example cracking. For instance, shrinkage caused during curing may cause internal stresses that can lead to cracks in the insulation. Cracking may also occur when the insulation material and underlying steel equipment are heated and cooled. During heating the inner surface of the insulation material (adjacent the hot steel equipment) expands more than the outer surface of the insulation material (adjacent the cold sea water). This differential expansion may also cause cracking. During cooling, the insulation material shrinks more and faster than the steel equipment, causing more cracking.

There exists a need for an improved and cost effective insulation materials and method to insulate subsea pipelines and equipment which reduces internal stresses and cracking in the molded insulation. SUMMARY OF THE INVENTION

The present invention is a cross-linked polyolefin composition and use thereof for insulating pipe joints and other subsea structures.

In one embodiment, the process of the present invention is a process for insulating a metallic pipe or metallic equipment comprising the step of injection molding a coating on the pipe or equipment wherein the coating comprises a cross-linkable mixture comprising:

(iii) one or more polyfunctional organopolysiloxane with a functional end group, preferably of the formula:

wherein Me is methyl and n is from 10 to 400,

preferably the polyfunctional organopolysiloxane (iii) is a hydroxyl-terminated

polydimethylsiloxane containing at least two hydroxyl end groups, a polydimethylsiloxane having at least two amine end groups, or a moisture-crosslinkable polysiloxane,

(iv) one or more cross-linking catalyst, preferably a Lewis or Bronsted acid or base, and (v) optionally one or more filler and/or additive.

In one embodiment of the process disclosed herein above, the silane is

copolymerized with ethylene in a reactor or grafted to an ethylene polymer by the use of an organic peroxide to provide a silane-grafted ethylene polymer.

Another embodiment of the process of the present invention is a process for re- insulating the connected portion of two plastic-insulated metallic pipes comprising the steps: (1) removing some plastic insulation from the end of each pipe, (2) connecting the ends of the pipes together to form a circular connected region having an external diameter, (3) fitting a split injection mold onto the connected region of the pipes, said injection mold having an internal diameter which is spaced from the external diameter of the of said connected region, (4) injecting cross-linkable polyolefin mixture into the cavity formed between said external diameter of the connected region and said internal diameter of the mold to obtain an injection-molded coating onto the connected region of the pipes, and (5) cooling the injection-molded coating and removing the injection mold, wherein the cross- linkable polyolefin mixture comprises: (i) one or more ethylene polymer, (ii) one or more silane, (iii) one or more polyfunctional organopolysiloxane with a functional end group, (iv) one or more cross-linking catalyst, and (v) optionally one or more filler and/or additive.

BRIEF DESCRIPTION OF DRAWINGS

FIG.l is a plot reporting data from a dynamic mechanical analysis (DMT A) of an example of the invention and three comparative examples not of the invention.

FIG.2 is a plot reporting data from a dynamic mechanical analysis (DMT A) of five examples of the invention and one comparative example not of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Many subsea pipelines and structures such as Christmas trees used for deep sea oil production and transportation require thermal insulation coatings to ensure proper flow of hot crude oil inside. One common method of providing insulation is by using multiple layers of polypropylene, comprising of layers that incorporate adhesive function, hollow glass spheres that provide insulation function, unmodified polypropylene that provides water barrier, mechanical integrity and impact resistance. These so called 5 layer polypropylene insulations (5LPP) are typically applied on long steel pipes typically varying in length from 10 to 25 m and diameter from 6" to 16". Such pipes are thenjoined together in the field by welding to string together entire pipelines. In order to prepare such a 'field joint' the insulation at the end of pipes is removed (this step typically achieved in the factory), the exposed pipe is cleaned, welded, cleaned again, an anticorrosion coat is applied. Traditionally, an insulation coating is applied by injection molding solid polypropylene. However, the injection molded polypropylene (IMPP) is typically different material than the polypropylenes used in the 5LPP insulation with different mechanical and physical properties. It is often observed that the combination of IMPP and 5LPP leads to failure (in the form of cracking) at the time of deployment of the pipeline in to offshore subsea applications, requiring costly and time consuming repairs, which have to be carried out offshore in difficult circumstances.

One embodiment of the present invention is a cross-linked polyolefin composition and use thereof for insulating pipe, preferably subsea pipe.

The cross-linkable polyolefin mixture of the present invention comprises, consists essentially of, or consists of (i) one or more ethylene polymer, (ii) one or more silane, (iii) one or more polyfunctional organopolysiloxane with a functional end group, (iv) one or more cross-linking cataslyst, and (v) optionally one or more filler and/or additive.

The pipe to be insulated may have any outside diameter, inside diameter, and length. The pipe has an outside surface and an inside surface.

Preferably the pipe and/or equipment to be coated are metallic.

In another embodiment of the method of the present invention, an insulation layer comprising, consisting essentially of, or consisting of the cross-linked polyolefin composition of the invention may be applied to subsea equipment other than pipe, for example a connector, a manifold, a tree, a pipeline end termination, a jumper, a valve, or other similar equipment.

Unless stated to the contrary, implicit from the context, or customary in the art, all parts and percents are based on weight and all test methods are current as of the filing date of this disclosure. For purposes of United States patent practice, the contents of any referenced patent, patent application or publication are incorporated by reference in their entirety (or its equivalent US version is so incorporated by reference) especially with respect to the disclosure of synthetic techniques, definitions (to the extent not inconsistent with any definitions specifically provided in this disclosure), and general knowledge in the art.

The numerical ranges in this disclosure are approximate, and thus may include values outside of the range unless otherwise indicated. Numerical ranges include all values from and including the lower and the upper values, in increments of one unit, provided that there is a separation of at least two units between any lower value and any higher value. As an example, if a compositional, physical or other property, such as, for example, molecular weight, viscosity, melt index, etc., is from 100 to 1,000, it is intended that all individual values, such as 100, 101, 102, etc., and sub ranges, such as 100 to 144, 155 to 170, 197 to 200, etc., are expressly enumerated. For ranges containing values which are less than one or containing fractional numbers greater than one (e.g., 1.1, 1.5, etc.), one unit is considered to be 0.0001, 0.001, 0.01 or 0.1, as appropriate. For ranges containing single digit numbers less than ten (e.g., 1 to 5), one unit is typically considered to be 0.1. These are only examples of what is specifically intended, and all possible combinations of numerical values between the lowest value and the highest value enumerated, are to be considered to be expressly stated in this disclosure. Numerical ranges are provided within this disclosure for, among other things, the component amounts of the composition and various process parameters.

"Polymer" means a compound prepared by reacting (i.e., polymerizing) monomers, whether of the same or a different type. The generic term polymer thus embraces the term "homopolymer", usually employed to refer to polymers prepared from only one type of monomer, and the term "interpolymer" as defined below.

"Interpolymer" and "copolymer" mean a polymer prepared by the polymerization of at least two different types of monomers. These generic terms include both classical copolymers, i.e., polymers prepared from two different types of monomers, and polymers prepared from more than two different types of monomers, e.g., terpolymers, tetrapolymers, etc.

"Ethylene- vinylsilane polymer" and like terms mean an ethylene polymer comprising silane functionality. The silane functionality can be the result of either polymerizing ethylene with a vinyl silane, e.g., a vinyl trialkoxy silane comonomer, or, grafting such a comonomer onto an ethylene polymer backbone as described, for example, in USP 3,646,155 or 6,048,935.

"Blend," "polymer blend" and like terms mean a blend of two or more polymers. Such a blend may or may not be miscible. Such a blend may or may not be phase separated. Such a blend may or may not contain one or more domain configurations, as determined from transmission electron spectroscopy, light scattering, x-ray scattering, and any other method known in the art.

"Composition" and like terms mean a mixture or blend of two or more components. For example, in the context of preparing a silane-grafted ethylene polymer, a composition would include at least one ethylene polymer, at least one vinyl silane, and at least one free radical initiator. In the context of preparing a cable sheath or other article of manufacture, a composition would include an ethylene-vinylsilane copolymer, a catalyst cure system and any desired additives such as lubricants, fillers, anti-oxidants and the like.

"Ambient conditions" and like terms means temperature, pressure and humidity of the surrounding area or environment of an article. The ambient conditions of a typical office building or laboratory include a temperature of 23 °C and atmospheric pressure.

"Catalytic amount" means an amount of catalyst necessary to promote the cross- linking of an ethylene-vinylsilane polymer at a detectable level, preferably at a

commercially acceptable level.

"Crosslinked", "cured" and similar terms mean that the polymer, before or after it is shaped into an article, was subjected or exposed to a treatment which induced cross-linking and has xylene or decalene extractables of less than or equal to 90 weight percent (i.e., greater than or equal to 10 weight percent gel content).

"Crosslinkable", "curable" and like terms means that the polymer, before or after shaped into an article, is not cured or crosslinked and has not been subjected or exposed to treatment that has induced substantial cross-linking although the polymer comprises additive(s) or functionality which will cause or promote substantial cross-linking upon subjection or exposure to such treatment (e.g., exposure to water).

"Melt-shaped" and like terms refer to an article made from a thermoplastic composition that has acquired a configuration as a result of processing in a mold or through a die while in a melted state. The melt-shaped article may be at least partially crosslinked to maintain the integrity of its configuration. Melt-shaped articles include pipe-joint insulation and the like.

Ethylene Polymers

The poly ethylenes used in the practice of this invention, i.e., the poly ethylenes that contain copolymerized silane functionality or are subsequently grafted with a silane, can be produced using conventional polyethylene polymerization technology, e.g., high-pressure, Ziegler-Natta, metallocene or constrained geometry catalysis. In one embodiment, the polyethylene is made using a high pressure process. In another embodiment, the polyethylene is made using a mono- or bis-cyclopentadienyl, indenyl, or fluorenyl transition metal (preferably Group 4) catalysts or constrained geometry catalysts (CGC) in combination with an activator, in a solution, slurry, or gas phase polymerization process. The catalyst is preferably mono-cyclopentadienyl, mono-indenyl or mono-fluorenyl CGC. The solution process is preferred. USP 5,064,802; WO93/19104; and WO95/00526 disclose constrained geometry metal complexes and methods for their preparation. Variously substituted indenyl containing metal complexes are taught in WO95/14024 and

W098/49212.

In general, polymerization can be accomplished at conditions well-known in the art for Ziegler-Natta or Kaminsky-Sinn type polymerization reactions, that is, at temperatures from 0-250°C, preferably 30-200°C, and pressures from atmospheric to 10,000 atmospheres (1013 megaPascal (MPa)). Suspension, solution, slurry, gas phase, solid state powder polymerization or other process conditions may be employed if desired. The catalyst can be supported or unsupported, and the composition of the support can vary widely. Silica, alumina or a polymer (especially poly(tetrafluoroethylene) or a polyolefin) are

representative supports, and desirably a support is employed when the catalyst is used in a gas phase polymerization process. The support is preferably employed in an amount sufficient to provide a weight ratio of catalyst (based on metal) to support within a range of from 1: 100,000 to 1: 10, more preferably from 1:50,000 to 1:20, and most preferably from 1:10,000 to 1:30. In most polymerization reactions, the molar ratio of catalyst to polymerizable compounds employed is from 10-12:1 to 10-1:1, more preferably from 10 "9 : 1 to 10 "5 :1.

Inert liquids serve as suitable solvents for polymerization. Examples include straight and branched-chain hydrocarbons such as isobutane, butane, pentane, hexane, heptane, octane, and mixtures thereof; cyclic and alicyclic hydrocarbons such as cyclohexane, cycloheptane, methylcyclohexane, methylcycloheptane, and mixtures thereof; perfluorinated hydrocarbons such as perfluorinated C4-10 alkanes; and aromatic and alkyl- substituted aromatic compounds such as benzene, toluene, xylene, and ethylbenzene.

The ethylene polymers useful in the practice of this invention include

ethylene/alpha-olefin interpolymers having a alpha-olefin content of between about 15, preferably at least about 20 and even more preferably at least about 25, wt % based on the weight of the interpolymer. These interpolymers typically have an alpha-olefin content of less than about 50, preferably less than about 45, more preferably less than about 40 and even more preferably less than about 35, wt % based on the weight of the interpolymer. The alpha-olefin content is measured by 13 C nuclear magnetic resonance (NMR) spectroscopy using the procedure described in Randall (Rev. Macromol. Chem. Phys., C29 (2&3)). Generally, the greater the alpha-olefin content of the interpolymer, the lower the density and the more amorphous the interpolymer, and this translates into desirable physical and chemical properties for the protective insulation layer.

The alpha-olefin is preferably a C3-20 linear, branched or cyclic alpha-olefin.

Examples of C3-20 alpha-olefins include propene, 1-butene, 4-methyl-l-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, and 1-octadecene. The alpha-olefins also can contain a cyclic structure such as cyclohexane or cyclopentane, resulting in an alpha-olefin such as 3 -cyclohexyl- 1 -propene (allyl cyclohexane) and vinyl cyclohexane. Although not alpha-olefins in the classical sense of the term, for purposes of this invention certain cyclic olefins, such as norbornene and related olefins, particularly 5- ethylidene-2-norbornene, are alpha-olefins and can be used in place of some or all of the alpha-olefins described above. Similarly, styrene and its related olefins (for example, alpha- methylstyrene, etc.) are alpha-olefins for purposes of this invention. Illustrative ethylene polymers include ethylene/propylene, ethylene/butene, ethylene/1 -hexene, ethylene/1 - octene, ethylene/styrene, and the like. Illustrative terpolymers include

The ethylene polymers used in the practice of this invention can be used alone or in combination with one or more other ethylene polymers, e.g., a blend of two or more ethylene polymers that differ from one another by monomer composition and content, catalytic method of preparation, etc. If the ethylene polymer is a blend of two or more ethylene polymers, then the ethylene polymer can be blended by any in-reactor or post- reactor process. The in-reactor blending processes are preferred to the post-reactor blending processes, and the processes using multiple reactors connected in series are the preferred in- reactor blending processes. These reactors can be charged with the same catalyst but operated at different conditions, e.g., different reactant concentrations, temperatures, pressures, etc, or operated at the same conditions but charged with different catalysts.

Any silane that will effectively copolymerize with ethylene, or graft to and crosslink an ethylene polymer, can be used in the practice of this invention, and those described by the following formula are exemplary:

O

CH 2 C f- CmH 2 m -)— (- C (· CnH 2 n) y ) x SiR : in which R 1 is a hydrogen atom or methyl group; x and y are 0 or 1 with the proviso that when x is 1, y is 1; m is an integer from 0 to 12 inclusive, preferably 0 to 4, n is an integer from 1 to 12 inclusive, preferably 1 to 4, and each R 2 independently is a hydrolyzable organic group such as an alkoxy group having from 1 to 12 carbon atoms (e.g. methoxy, ethoxy, butoxy), aryloxy group (e.g. phenoxy), araloxy group (e.g. benzyloxy), aliphatic acyloxy group having from 1 to 12 carbon atoms (e.g. formyloxy, acetyloxy,

propanoyloxy), amino or substituted amino groups (alkylamino, arylamino), or a lower alkyl group having 1 to 6 carbon atoms inclusive, with the proviso that not more than one of the three R groups is an alkyl. Such silanes may be copolymerized with ethylene in a reactor, such as a high pressure process. Such silanes may also be grafted to a suitable ethylene polymer by the use of a suitable quantity of organic peroxide, either before or during a shaping or molding operation. The ethylene polymers containing a copolymerized or grafted silane are herein referred to as a silane grafted or copolymerized polyethylene. Additional ingredients such as antioxidants, heat and light stabilizers, pigments, etc., also may be included in the formulation. The phase of the process during which the crosslinks are created is commonly referred to as the "cure phase" and the process itself is commonly referred to as "curing". Also included are silanes that add to unsaturation in the polymer via free radical processes such as mercaptopropyl trialkoxy silane.

Suitable silanes include silane-grafted polyolefins or silane-copolymerized polyolefins. Suitable silanes include, but are not limited to, unsaturated silanes that comprise an ethylenically unsaturated hydrocarbyl group, such as a vinyl, allyl, isopropenyl, butenyl, cyclohexenyl or gamma-(meth)acryloxy allyl group, or sorboyloxypropyl group and a hydrolyzable group, such as, for example, a hydrocarbyloxy, hydrocarbonyloxy, or hydrocarbylamino group. Examples of hydrolyzable groups include methoxy, ethoxy, formyloxy, acetoxy, proprionyloxy, and alkyl or arylamino groups. Preferred silanes are the unsaturated alkoxy silanes which can be grafted onto the polymer or copolymerized in- reactor with other monomers (such as ethylene and acrylates). These silanes and their method of preparation are more fully described in USP 5,266,627 to Meverden, et al. Vinyl trimethoxy silane (VTMS), vinyl triethoxy silane, vinyl triacetoxy silane, gamma- (meth)acryloxy propyl trimethoxy silane and mixtures of these silanes are the preferred silane crosslinkers for use in this invention. If filler is present, then preferably the crosslinker includes vinyl trialkoxy silane.

The amount of silane crosslinker used in the practice of this invention can vary widely depending upon the nature of the polymer, the silane, the processing or reactor conditions, the grafting or copolymerization efficiency, the ultimate application, and similar factors, but typically at least 0.5, preferably at least 0.7, weight percent is used.

Considerations of convenience and economy are two of the principal limitations on the maximum amount of silane crosslinker used in the practice of this invention, and typically the maximum amount of silane crosslinker does not exceed 5, preferably it does not exceed 3, weight percent.

The silane crosslinker is grafted to the polymer by any conventional method, typically in the presence of a free radical initiator, e.g., peroxides or azo compounds, or by ionizing radiation, etc. Organic initiators are preferred, such as any one of the peroxide initiators, for example, dicumyl peroxide, di-tert-butyl peroxide, t-butyl perbenzoate, benzoyl peroxide, cumene hydroperoxide, t-butyl peroctoate, methyl ethyl ketone peroxide, 2,5-dimethyl-2,5-di(t-butyl peroxy)hexane, lauryl peroxide, and tert-butyl peracetate. A suitable azo compound is 2,2-azobisisobutyronitrile. The amount of initiator can vary, but it is typically present in an amount of at least 0.04, preferably at least 0.06, parts per hundred resin (phr). Typically, the initiator does not exceed 0.15, preferably it does not exceed about 0.10, phr. The weight ratio of silane crosslinker to initiator also can vary widely, but the typical crosslinker: initiator weight ratio is between 10:1 to 500:1, preferably between 18: 1 and 250: 1. As used in parts per hundred resin or phr, "resin" means the olefinic polymer.

While any conventional method can be used to graft the silane crosslinker to the polyolefin polymer, one preferred method is blending the two with the initiator in the first stage of a reactor extruder, such as a Buss kneader or a twin screw extruder. The grafting conditions can vary, but the melt temperatures are typically between 160 and 260°C, preferably between 190 and 230°C, depending upon the residence time and the half life of the initiator.

Copolymerization of vinyl trialkoxysilane crosslinkers with ethylene and other monomers may be done in a high-pressure reactor that is used in the manufacture of ethylene homopolymers and copolymers with vinyl acetate and acrylates.

Polyfunctional Organopolysiloxane with Functional End Groups

The oligomers containing functional end groups useful in the present process comprise from 2 to 100,000 or more units of the formula R2S1O in which each R is independently selected from a group consisting of alkyl radicals comprising one to 12 carbon atoms, alkenyl radicals comprising two to about 12 carbon atoms, aryls, and fluorine substituted alkyl radicals comprising one to about 12 carbon atoms. The radical R can be, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, dodecyl, vinyl, allyl, phenyl, naphthyl, tolyl, and 3,3,3-trifluoropropyl. Preferred is when each radical R is methyl.

In one embodiment, the organopolysiloxane containing one or more functional end groups is a hydroxyl-terminated polydimethylsiloxane containing at least two hydroxyl end groups. Such polydimethylsiloxanes are commercially available, for example as silanol- terminated polydimethylsiloxane from The Dow Chemical Company. However, polydimethylsiloxanes having at least two other terminal groups that can react with grafted silanes may be used e.g. polydimethylsiloxanes with amine end groups and the like. In addition, the polysiloxane may be a moisture-crosslinkable polysiloxane. In preferred embodiments, the polydimethylsiloxane is of the formula

in which Me is methyl and n is in the range of 2 to 100,000 or more, preferably in the range of 10 to 400 and more preferably in the range of 20 to 120. Examples of suitable polyfunctional organopolysiloxanes are the silanol-terminated polydimethylsiloxane DMS- 15 (Mn of 2,000-3,500, viscosity of 45-85 centistokes, -OH level of 0.9-1.2%) from Gelest Corp., and Silanol Fluid 1-3563 (viscosity 55-90 centistokes, -OH level of 1-1.7%) from The Dow Chemical Company. In some embodiments the polyfunctional

organopolysiloxane comprises branches such as those imparted by Me-Si03/2 or Si0 4 /2 groups (known as T or Q groups to those skilled in silicone chemistry).

The amount of polyfunctional organopolysiloxane used in the practice of this invention can vary widely depending upon the nature of the polymer, the silane, the polyfunctional organopolysiloxane, the processing or reactor conditions, the ultimate application, and similar factors, but typically at least 0.5, preferably at least 2, weight percent is used. Considerations of convenience and economy are two of the principal limitations on the maximum amount of polyfunctional organopolysiloxane used in the practice of this invention, and typically the maximum amount of polyfunctional organopolysiloxane does not exceed 20, preferably it does not exceed 10, weight percent.

Cross-linking Catalyst

Cross-linking technology is well known, for example see USP 8835548, USP 8991039, and USP 9387625 all of which are incorporated by reference in their entirety. Cross-linking catalysts include the Lewis and Bronsted acids and bases. Lewis acids are chemical species that can accept an electron pair from a Lewis base. Lewis bases are chemical species that can donate an electron pair to a Lewis acid. Lewis acids that can be used in the practice of this invention include the tin carboxylates such as dibutyl tin dilaurate (DBTDL), dimethyl hydroxy tin oleate, dioctyl tin maleate, di-n-butyl tin maleate, dibutyl tin diacetate, dibutyl tin dioctoate, stannous acetate, stannous octoate, and various other organo-metal compounds such as lead naphthenate, zinc caprylate and cobalt naphthenate. DBTDL is a preferred Lewis acid. Lewis bases that can be used in the practice of this invention include, but are not limited to, the primary, secondary and tertiary amines. These catalysts are typically used in moisture cure applications.

Bronsted acids are chemical species that can lose or donate a hydrogen ion (proton) to a Bronsted base. Bronsted bases are chemical species that can gain or accept a hydrogen ion from a Bronsted acid. Bronsted acids that can be used in the practice of this invention include sulfonic acid.

The minimum amount of cross-linking catalyst used in the practice of this invention is a catalytic amount. Typically this amount is at least 0.01, preferably at least 0.02 and more preferably at least 0.03, weight percent (wt %) of the combined weight of the total composition. The only limit on the maximum amount of cross-linking catalyst in the ethylene polymer is that imposed by economics and practicality (e.g., diminishing returns), but typically a general maximum comprises less than 5, preferably less than 3 and more preferably less than 2, wt % of the combined weight of the total composition.

Fillers and Additives

The composition from which the crosslinked article, e.g., pipe insulation layer, is made can be filled or unfilled. If filled, then the amount of filler present should preferably not exceed an amount that would cause unacceptably large degradation of the thermal and/or mechanical properties of the silane-crosslinked, ethylene polymer. Typically, the amount of filler present is between 2 and 80, preferably between 5 and 70, weight percent (wt %) based on the total weight of the composition. Representative fillers include kaolin clay, magnesium hydroxide, silica, calcium carbonate, hollow glass microspheres, and carbon blacks. The filler may or may not have flame retardant properties. In a preferred embodiment of this invention in which filler is present, the filler is hollow glass microspheres, which reduce the specific gravity and thermal conductivity of the resulting compound. Filler and catalyst are selected to avoid any undesired interactions and reactions, and this selection is well within the skill of the ordinary artisan.

The compositions of this invention can also contain additives such as, for example, antioxidants (e.g., hindered phenols such as, for example, IRGANOX™ 1010 a registered trademark of Ciba Specialty Chemicals), phosphites (e.g., IRGAFOS™ 168 a registered trademark of Ciba Specialty Chemicals), UV stabilizers, cling additives, light stabilizers (such as hindered amines), plasticizers (such as dioctylphthalate or epoxidized soy bean oil), scorch inhibitors, mold release agents, tackifiers (such as hydrocarbon tackifiers), waxes (such as polyethylene waxes), processing aids (such as oils, organic acids such as stearic acid, metal salts of organic acids), oil extenders (such as paraffin oil and mineral oil), colorants or pigments to the extent that they do not interfere with desired physical or mechanical properties of the compositions of the present invention. These additives are used in amounts known to those versed in the art.

Cross-linking is promoted by the addition of a catalyst to the mixture before or during melt-shaping. Surprisingly, compounding a cross-linkable mixture containing (i) one or more ethylene polymer, (ii) one or more one or more silane, (iii) one or more polyfunctional organopolysiloxane with a functional end group, (iv) one or more cross- linking cataslyst, and (v) optionally one or more filler and/or additive, produces a stable thermoplastic composition which can be used in fabrication requiring melt processing, such as injection molding, but then will subsequently become crosslink after the injection molding step.

In one embodiment, the process of the present invention is a process for insulating a metallic pipe, preferably a metallic subsea pipe, and/or other metallic equipment other than pipe and comprises the step of injection molding a coating on said metallic pipe or equipment wherein the coating comprises a cross-linkable mixture comprising: (i) one or more ethylene polymer, (ii) one or more silane, (iii) one or more polyfunctional

organopolysiloxane with a functional end group, (iv) one or more cross-linking catalyst, and (v) optionally one or more filler and/or additive.

In another embodiment of the process of the present invention, the cross-linked polyolefin composition can be conveniently used for forming a re-insulating injection- molded coating on the connected portion of plastic-insulated metallic pipes. Accordingly, a further object of the present invention is a process for re-insulating the connected portion of two plastic-insulated metallic pipes, said process comprising the following steps: (1) removing some plastic insulation from the end of each pipe; (2) connecting the ends of the pipes together to form a circular connected region having an external diameter; (3) fitting a split injection mold onto the connected region of the pipes, said injection mold having an internal diameter which is spaced from the external diameter of the of said connected region; (4) injecting a cross-linkable polyolefin composition into the cavity formed between said external diameter of the connected region and said internal diameter of the mold to obtain an injection-molded coating onto the connected region of the pipes and (5) cooling the injection-molded coating and removing the injection mold.

Normally, steps (1) and (2) are carried out according methods well known in the art. In particular, for plastic insulated metallic pipes, the connecting step (2) is carried out by welding together the ends of the two pipes deprived of the plastic insulating layer, thereby forming a weld seam. Before step (3) is carried out, the connected region can be conveniently blasted with known techniques to remove any surface imperfection and optionally, but preferably, known primers and polymer adhesives may be applied onto the connected region to promote the adhesion of the coating applied in step (4).

In step (4) a coating is formed onto the connected region of the connected metallic pipes, replacing the plastic insulating layer removed in step (1) and thereby re-insulating the metallic pipes. The coating formed in step (4) may partially overlap the existing plastic insulation of the metallic pipes. The melted cross -linkable polyolefin composition is normally injected into the mold with a pressure of less than 25 MPa and a temperature not exceeding 230°C. Preferred injection molds, injection molding and cooling conditions to be used in steps (3) to (5) are described in USP 6,843,950.

It has surprisingly been found that when cross-linkable polyolefin composition are used in the process described above, it is possible to produce a thick and uniform injection- molded coating on the connected region of plastic-insulated metallic pipes. The injection- molded coating obtained with the re-insulating process described above is at least 10 mm, preferably up to 80 mm, more preferably up to 110 mm thick. Moreover, the cross-linkable polyolefin composition, after it becomes cross-linked, shows a good adhesion to the corrosion coating of the metallic pipe.

In one embodiment of the process of the present invention, the pipe is cleaned prior to step (3). Cleaning methods include surface dust wiping off, surface sanding, surface dissolve cleaning, scraping, and the like. Any suitable cleaning solution and/or procedure used for cleaning such pipe can be used.

In another embodiment of the process of the present invention, a protective coating is applied to the pipe before the step (3). Preferably, the protective coating is applied after the pipe is cleaned but before the preform is provided. Examples of a protective coating are an anti corrosion coating and an adhesion promoting coating.

In one embodiment of the process of the invention described herein above the cross- linkable mixture is useful for thermal insulation for subsea oil and gas applications. Although a pipe is insulated in one embodiment of the present invention, any subsea equipment that can be surrounded by a mold may be insulated by certain embodiments of the present invention. EXAMPLES

The following components are used in Examples 1 to 5 and Comparative Examples

A to C.

"INFUSE 9010" is an ethylene/alpha olefin copolymer with a melt index of 0.5 g/10 min at 190°C and under a load of 2.16 kg and a density of 0.877 g/cm 3 available from The Dow Chemical Company;

"VERSIFY 2000" is an ethylene/propylene block copolymer with a melt index of 2 g/10 min at 230°C and under a load of 2.16 kg and a density of 0.888 g/cm 3 available from The Dow Chemical Company;

"VTMS" is vinyltrimethoxy silane available from The Dow Chemical Company;

"DMS-S15" which is a hydroxyl-terminated polydimethoxysiloxane available from Gelest, Inc;

" LUPEROX™ 101" is [(2,5-dimethyl-2,5-di(t-butylperoxy)hexane] available from Arkema;

"BORCOAT™ EA 165E" is a commonly used subsea field joint material comprising an elastomer modified compound, based on a high molecular weight polypropylene available from Borealis;

and

"HIFAX™ CA197J" " is a commonly used subsea field joint material comprising a medium melt flow, unfilled, polypropylene copolymer available from Lyondell Basell.

The compositions of Examples 1 to 5 and Comparative Examples A to C are shown in Table 1, values are in weight percent based on the total weight of the composition. Table 1

Examples 1 to 5 and Comparative Example A.

Pellets of the ethylene/alpha olefin block copolymer and the ethylene/propylene block copolymers are compounded with the vinyltrimethoxy silane (VTMS) and [(2,5- dimethyl-2,5-di(t-butylperoxy)hexane] (LUPEROX 101) in a Coperion ZSK-25MC twin- screw reactive extruder, with temperatures ranging from 200°C to 270°C. The VTMS and LUPEROX 101 are injected in the extruder when the polymer temperature is in the range of 220 to 260°C. Unreacted VTMS and peroxide byproducts are stripped by a vacuum line trap in the penultimate section of the extruder barrel. The polymer melt is extruded through a die into a Gala underwater pelletizing system forming a first compounded material (a silane grafted polyolefin), it is pelletized, collected, and refed into the extruder where it is compounded with silanol terminated polydimethylsiloxane (DMS-S15) to form a second compounded material. The second compounded material is extruded through a die into a Gala underwater pelletizing system and pelletized. The pelletized second compounded material is compounded with the catalyst masterbatch Dow SI- LINK DFDA-5481 NT to form a third compounded material.

Dynamic mechanical thermal analysis (DMT A) for Example 4 and Comparative Examples A, B, and C are shown in FIG. 1. The Comparative Examples melt between 120 to 160°C, at which point they show a precipitous drop in modulus. In FIG. 2, DMTA analysis for Examples 1 to 5 and Comparative Example A is shown. As can be seen, they exhibit a plateau modulus beyond 180°C, whereas the Comparative Example A (which doesn't contain either DMS-S15 or cross-linking catalyst) melt near 120°C, at which point it shows a precipitous drop in modulus.